In the installation of wall and floor covering surfaces such as ceramic tile and the like, slate, marble and the like, numerous compositions have been developed which utilize a hydraulic cement, such as Portland cement, as the principal factor in the bonding adhesives. Ordinary Portland cement per se, or together with sand or limestone fillers, is generally not preferred for this purpose since it does not have the ability to retain the water used in mixing it for sufficient time to enable an adequate bonding cure to occur. In order to overcome this disadvantage, there was developed a type of adhesive now known in the art as dry-set Portland cement mortar. These mortars possess certain advantageous properties: they may be exposed to air after mixing with water for a period of time; they may be applied to the substrates without undue hurry; they remain plastic for a sufficient period of time to permit small movements to be made in the tile installation after the initial tile to substrate surface contact; they develop strong bonding between the tile or similar surfacing and the substrate surface to which it is bonded; and they possess a reasonably predictable initial set time, minimum drying shrinkage, and some sag resistance. A number of such dry-set compositions have been developed, including those which are disclosed in U.S. Pat. No. 2,820,713.
One of the many properties required by cementitious compositions which are useful in the setting of tiles is that the composition be sag resistant. As used herein, the term "sag resistance" is intended to mean the property or characteristic of an adhesive composition to resist movement under load until a certain load level is reached. This property is important in dry-set mortars and in latex Portland cement mortars; for example, since a mortar to be practically functional must be in a slurry or paste form, on the one hand, but also must be capable of supporting the load imposed upon it during setting, on the other hand. Thus, it is vital that the mortar support a tile without any appreciable sinking of the tile into the mortar during the period in which the mortar sets or hardens. In wall applications, sag resistance is even more important because the mortar must hold the tile in position on the wall during the setting period.
In the course of development of dry-set mortars, i.e., mortars based on the use of a water retentive agent which set or harden upon the addition of water, it has been found that the sag resistance could be substantially improved by the addition of fibrous materials, such as asbestos fibers. Since the time of this initial discovery, it has been desirable to find substitutes for some of these fibrous materials, especially asbestos fiber. In U.S. Application Ser. No. 749,946, filed Dec. 20, 1976, assigned to the same assignee as herein, now U.S. Pat. No. 4,082,563 there are disclosed sag-resistant dry-set cementitious hydraulic compositions based on the use of certain salts which, under appropriate conditions, form gelatinous or hydrated hydroxides. These additives are non-fibrous, non-toxic and, in addition, provide sag resistance properties comparable to those imparted by asbestos fibers. The compositions of Ser. No. 749,946 include an hydraulic cement and a water retentive agent or agents.
The use of certain metal salts in other types of cementitious compositions for specific purposes other than to provide sag resistance has been proposed in the art. In U.S. Pat. No. 1,901,890 to Barnhart, for instance, a mixture of certain sulfates, e.g., sulfates of alkali metals, aluminum and manganese, are taught for the purpose of creating a glaze-forming and waterproofing composition for cementitious materials. In U.S. Pat. No. 2,890,965 to Underdown, it is proposed that certain salts, inter alia, aluminum sulfate, improve the plasticity and flowability of certain cementitious materials. The use of certain aluminum, iron and chromium salts is disclosed in U.S. Pat. No. 2,390,138 to Vallandigham for the purpose of accelerating the setting of alginate salts used in the manufacture of dental casts.
Other uses are disclosed elsewhere in the art. In U.S. Pat. No. 3,114,647 to Mecham, it is disclosed that certain double metal salts, i.e., salts of ammonium and trivalent metals such as aluminum, iron, manganese and chromium, as well as aluminum sulfate, increase the hardness of materials made from Portland cement. Mecham also specifies the use of sulfuric acid as well as calcium chloride as being necessary to achieve the desired effect.
U.S. Pat. No. 3,313,638 to Konrad discloses the use of low concentrations of aluminum chloride in compositions for castable refractory material with reduced physical separation of cement from calcined kaolin clays.
U.S. Pat. No. 3,782,991 to Burge discloses the specific use of anhydrous aluminum sulfate as an accelerator for low temperature concreting.
Prior to the discovery disclosed in U.S. application Ser. No. 749,946, however, it was not previously recognized in the art that certain metals salts capable of forming gelatinous or hydrated hydroxides are effective in imparting sag resistance to dry-set cementitious mortar compositions.